The official iTunes site says "The official Jon Stewart and Stephen Colbert-approved app of the Rally to Restore Sanity and/or Fear.
Download it before you board the sanity bus and/or fear wagon to D.C. Features include a map of the Rally site, links to Facebook, Twitter and Foursquare, a portal to upload photos to the official Rally photostream and an exclusive welcome message from Jon and Stephen themselves!"
Pretty awesome, isn't it? Not only is the application great for those attending the rally, but it's also great for all those at home who will be following the rally from home.